Piezoelectric actuators generally consist of collectively sintered stacks of piezoceramic layers with interposed metal electrodes. Every second metal electrode is brought out on a first side and connected to a first metallization path. On the opposite side there is provided a second metallization path which is connected in an electrically conducting manner to the other metal electrodes, thereby providing two metal electrode arrangements which are electrically isolated from one another.
During operation of the piezoelectric actuators, large forces but only small relative displacements are attained, parallel to a polarization direction of the piezoceramic layers. To achieve low operating voltages, the piezoelectric actuator consists of a plurality of piezoceramic layers. To polarize the actuator, an electric polarization field is applied to the two electrode structures, thereby producing a maximum remanent polarization and an ordered distribution of the domains oriented in field direction in the crystals of the ceramic layers compared to an unpolarized initial state. Polarization is performed at a piezoceramic layer temperature above the Curie temperature of the piezoceramic layer.
For electrical contacting of the piezoelectric actuator, it is additionally necessary to contact the metallization paths to electric conductors. For this purpose the electric conductors are permanently soldered to the metallization paths in a soldering process.
European patent application EP 0 350 941 A2 discloses a piezoelectric actuator and a method for manufacturing the piezoelectric actuator which is designed in the form of a plurality of piezoceramic layers, an electrode being disposed between each of the piezoceramic layers. Every second electrode is connected in an electrically conducting manner to a metallization path which is disposed on the outside of the piezoelectric actuator. The other electrodes are connected in an electrically conducting manner to a second metallization path which is disposed opposite the first metallization path on the outside of the piezoelectric actuator. For a connection process, the piezoelectric actuator is heated above the Curie temperature so that a chemical bond is formed between the electrodes and the piezoceramic layers. In a following cooling process, polarization of the piezoceramic layers is performed, the temperature of the piezoceramic layers still being above the Curie temperature. In a subsequent soldering process, electric conductors are soldered to the metallization paths.
German patent application DE 100 26 635 A1 describes a method for producing a soldered joint between an electrical contact area of a piezoceramic actuator and a wire surface, wherein metallization strips of the piezoelectric actuator are soldered to wires disposed in parallel. Soldering takes place after polarization of the piezoceramic actuator. During the soldering process, the piezoceramic actuator is at a temperature below the Curie temperature.